The broad objectives of this proposal are to investigate the mechanistic basis for microtubule movement and direction of microtubule movement by kinesin-like microtubule motor proteins, particularly the ncd protein. The strategy will be to compare and contrast molecular details of ncd structure and motility with kinesin structure and motility. The specific aims of the proposal are to conduct quantitative single- molecule motility experiments with ncd and kinesin under identical experimental conditions. A multiple-beam optical tweezer-based instrument capable of nanometer spatial resolution and piconewton-scale force measurements will be used to determine for ncd and kinesin the magnitude and kinetics of single translocation on events, the force profile during the translocation cycle, and the path over the microtubule surface. Precise measurement of the mechanical parameters of ncd and kinesin will be used to establish a basis for genetic manipulations aimed at ncd and kinesin.